Currently available positioning systems typically include multiple sensors organized into discrete systems. For example, a Global Navigation Satellite System (GNSS) is typically deployed as one discrete system, a Distance Measurement Equipment (DME) system is typically deployed as another discrete system, an inertial reference system is typically deployed as another discrete system, and the VHF Omnidirectional-Range (VOR) as yet another discrete system. In addition, detecting specific GNSS satellite system failures, sometimes referred to as evil waveform monitoring, conventionally relies on ground based monitoring stations which share system failure information either via a Notice to Airmen (NOTAM) or are relayed directly to a vehicle using a notification system such as the Space Based Augmentation Service (SBAS).
The precision of the position is continuously monitored onboard many vehicles since specific airspace access is conditional on the monitored positioning performance. For example, a specific track in continental airspace may require a positioning system onboard an aircraft desiring airspace access to maintain a Required Navigation Performance (RNP) value of 5.0 nautical miles (NM). Should the Actual Navigation Performance (ANP) of onboard positioning systems be unable to comply with the RNP value of 5.0, published standards may disallow the aircraft from entering or continuing on the specific track.
Precision position sensing required for enhanced airspace operations, such as RNP, often requires integration of positioning information from a combination of these discrete sensor systems. System integration can require costly additional hardware, custom software, wiring and cable interfaces. The resulting “blended” precision position is reported as the ANP. At the same time, pressure continues to mount to reduce the size, weight, power and cost (SWaPC) of airborne positioning systems.
High density, complex aircraft operations may rely on precise positioning to meet the RNP established for a particular airspace. For example, to begin a specific instrument approach to a specific runway, an aircraft positioning system may be required to maintain an RNP value of 0.3 NM. Should the ANP of positioning systems and methods be unable to accurately position the aircraft within this RNP, published statutory regulation may prohibit the aircraft from beginning the approach. To meet such performance requirements, prior art precision position sensing methods may utilize multiple, discrete integrated sensors to meet the operational requirements for enhanced airspace operations. (e.g. RNP/ANP, approach, landing, etc.) Pressure from regulators and aircraft integrators to improve the availability and reliability of vehicle positioning methods and systems as well as reduction in size, weight, required power, and cost (SWaPC) may require an enhanced alternative.
In order to meet the integrity requirements for these operations, airborne receivers are currently aided by offboard augmentation solutions. Such offboard augmentation may include the aforementioned SBAS and a Ground Based Augmentation System (GBAS). Without these offboard augmentation systems, inaccurate signals may adversely affect precise positioning systems. Evil waveforms, outages (both planned and unplanned), atmospheric anomalies, jamming (both self and hostile) are many of the threats that may be monitored by these systems.
In addition, traditional onboard positioning systems benefiting from offboard augmentation may require additional receiving equipment onboard the vehicle. For example, a Localizer Performance with Vertical guidance (LPV) approach may require onboard WAAS receiver installation to enable accurate LPV navigation. Such WAAS or Local Area Augmentation System (LAAS) may require an additional Very High Frequency (VHF) Data Broadcast (VDB) receiver mounted on the vehicle to ensure reception of augmentation signals.
There is, therefore, a continuing need for new on-vehicle alternatives to improve positioning precision and integrity without the use of ground or space based augmentation solutions. This solution needs to mindful of the cost of increases in size and weight and should strive for reduced size, weight, power, and cost of the positioning systems. With multi-frequency and multi-constellation capability, a desirable method and system may provide signal monitoring and erroneous signal exclusion performed autonomously (e.g. onboard the vehicle) without offboard augmentation.